Power receiver and power transmitting system

ABSTRACT

A power receiver includes a first secondary-side resonant coil that receives electric power from a primary-side resonant coil through magnetic field resonance; a rectifier circuit that rectifies alternating-current power; a smoothing circuit; a pair of output terminals; a switch, inserted in series on a line between the rectifier circuit and the smoothing circuit, that switches a state of the line, and a drive controller that drives the switch through a first PWM drive pattern determined by a first duty cycle and a first frequency that is less than or equal to a frequency of the magnetic field resonance. The first duty cycle is set based on a first power reception efficiency of the first secondary-side resonant coil, a first rated output of a first load, a second power reception efficiency of a second secondary-side resonant coil of another power receiver, and a second rated output of a second load.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of International Application PCT/JP2014/075420 filed on Sep. 25, 2014 and designated the U.S., the entire contents of which are incorporated herein by reference.

FIELD

The embodiment discussed herein relates to a power receiver and a power transmitting system.

BACKGROUND

Conventionally, there exists a contactless power receiving apparatus including: a resonance element adapted to receive supply of alternating-current power in a contactless fashion by resonance from a resonance element of a power supplying source; an excitation element adapted to receive supply of the alternating-current power by electromagnetic induction from the resonance element; a rectification circuit adapted to generate direct-current power from the alternating-current power from the excitation element and output the direct-current power; and a changeover circuit adapted to change over the alternating-current power between a supply state and a non-supply state to the rectification circuit (see Patent Document 1, for example).

However, for the conventional contactless power receiving apparatus (power receiver), an efficiency of electric power reception when the resonance element receives electric power transmitted to the power receiver is not considered. Because the efficiency of electric power reception is changed depending on a position, orientation, or the like of the power receiver with respect to a power transmitter, when electric power is transmitted without considering the efficiency of electric power reception especially in a case where a plurality of power receivers are, it may become impossible to supply the electric power to the plurality of power receivers in a balanced manner.

RELATED-ART DOCUMENTS Patent Documents

-   [Patent Document 1] Japanese Laid-open Patent Publication No.     2011-019291

SUMMARY

According to an aspect of the embodiments, a power receiver includes: a first secondary-side resonant coil, including a first terminal and a second terminal, that receives electric power from a primary-side resonant coil through magnetic field resonance generated between the primary-side resonant coil and the first secondary-side resonant coil; a rectifier circuit, coupled to the first terminal and the second terminal, that rectifies alternating-current power input from the first secondary-side resonant coil; a smoothing circuit coupled to an output side of the rectifier circuit; a pair of output terminals coupled to an output side of the smoothing circuit; a switch, inserted in series in a line between the rectifier circuit and the smoothing circuit, that switches a coupling state of the line, and a drive controller that drives the switch through a first PWM drive pattern determined by a first duty cycle and by a first frequency that is less than or equal to a frequency of the magnetic field resonance. The first duty cycle is set based on a first efficiency of electric power reception of the first secondary-side resonant coil, a first rated output of a first load coupled to the pair of output terminals, a second efficiency of electric power reception of a second secondary-side resonant coil of another power receiver that receives electric power from the primary-side resonant coil through magnetic field resonance generated between the primary-side resonant coil and the second secondary-side resonant coil, and a second rated output of a second load to which electric power is supplied from the other power receiver.

The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a power transmitting system 50;

FIG. 2 is a diagram illustrating a state in which electric power is transmitted from a power transmitter 10 to electronic devices 40A and 40B through magnetic-field resonance;

FIG. 3 is a diagram illustrating a state in which electric power is transmitted from the power transmitter 10 to electronic devices 40B1 and 40B2 through magnetic-field resonance;

FIG. 4 is a diagram illustrating a power transmitting apparatus 80 and a power receiver 100 according to an embodiment;

FIG. 5 is a diagram illustrating electronic devices 200A and 200B and the power transmitting apparatus 80 using a power transmitting system 500 according to the embodiment;

FIG. 6 is a diagram illustrating a relationship between efficiencies of electric power reception and duty cycles of power receivers 100A and 100B;

FIG. 7 is a diagram illustrating a relationship between a duty cycle of a PWM drive pattern and received electric power in the power receiver 100;

FIG. 8 is a task diagram illustrating processing that the power transmitter 10 and the power receivers 100A and 100B execute for setting the duty cycles;

FIG. 9 is a diagram illustrating equivalent circuits of the power transmitting apparatus 80 and the electronic devices 200A and 200B;

FIGS. 10A and 10B are diagrams illustrating table data that associates duty cycles with relationships between mutual inductances M_(TA) and mutual inductances M_(TB);

FIGS. 11A and 11B are diagrams illustrating table data that associate efficiencies of electric power reception with mutual inductances M_(TA) and M_(TB);

FIG. 12 is a flowchart illustrating a method in which the power transmitter 10 sets the duty cycle according to the embodiment; and

FIG. 13 is a diagram illustrating a power receiver 101 according to a variation example of the embodiment.

DESCRIPTION OF EMBODIMENT

Hereinafter, an embodiment, to which power receivers and a power transmitting system of the present invention are applied, will be described.

An object is to provide a power receiver and a power transmitting system that can improve a supply balance of electric power.

Embodiment

Before describing the embodiment to which the power receivers and the power transmitting system of the present invention are applied, a technical premise of the power transmitting system and the power receivers according to the embodiment is described with reference to FIGS. 1 to 3.

FIG. 1 is a diagram illustrating a power transmitting system 50.

As illustrated in FIG. 1, the power transmitting system 50 includes an alternating-current (AC) power source 1, a primary-side (power transmitting side) power transmitter 10, and a secondary-side (power receiving side) power receiver 20. The power transmitting system 50 may include a plurality of power transmitters 10 and a plurality of power receivers 20.

The power transmitter 10 includes a primary-side coil 11 and a primary-side resonant coil 12. The power receiver 20 includes a secondary-side resonant coil 21 and a secondary-side coil 22. A load device 30 is coupled to the secondary-side coil 22.

As illustrated in FIG. 1, the power transmitter 10 and the power receiver 20 perform transmission of energy (electric power) from the power transmitter 10 to the power receiver 20 through magnetic-field resonance (magnetic-field sympathetic vibration) between the primary-side resonant coil (LC resonator) 12 and the power receiving resonant coil (LC resonator) 21. Here, the electric power can be transmitted from the primary-side resonant coil 12 to the secondary-side resonant coil 21 by not only the magnetic-field resonance but also by electric field resonance (electric field sympathetic vibration) or the like. In the following description, the magnetic-field resonance will be mainly described as an example.

In the first embodiment, for example, a case is described where a frequency of an AC voltage that the AC power source 1 outputs is 6.78 MHz and a resonance frequency of the primary-side resonant coil 12 and the secondary-side resonant coil 21 is 6.78 MHz.

Note that the power transmission from the primary-side coil 11 to the primary-side resonant coil 12 is performed by utilizing electromagnetic induction. Also, the power transmission from the secondary-side resonant coil 21 to the secondary-side coil 22 is performed by utilizing the electromagnetic induction.

Although FIG. 1 illustrates a configuration in which the power transmitting system 50 includes the secondary-side coil 22, the power transmitting system 50 is not required to include the secondary-side coil 22. In this case, the load device 30 may be directly coupled to the secondary-side resonant coil 21.

FIG. 2 is a diagram illustrating a state where electric power is transmitted from the power transmitter 10 to electronic devices 40A and 40B through magnetic-field resonance.

The electronic devices 40A and 40B are a tablet computer and a smartphone, respectively, and include power receivers 20A and 20B, respectively. Each of the power receivers 20A and 20B has a configuration where the secondary-side coil 22 is removed from the power receiver 20 (see FIG. 1) illustrated in FIG. 1. That is, each of the power receivers 20A and 20B includes the secondary-side resonant coil 21. Note that although the simplified power transmitter 10 is illustrated in FIG. 2, the power transmitter 10 is coupled to the AC power source 1 (see FIG. 1).

In FIG. 2, each of the electronic devices 40A and 40B is arranged at an equal distance from the power transmitter 10. The power receivers 20A and 20B included in the respective electronic devices 40A and 40B receive the electric power from the power transmitter 10 through the magnetic-field resonance in a non-contact state.

Here, for example, in a state illustrated in FIG. 2, an efficiency of electric power reception of the power receiver 20A included in the electronic device 40A is 40%, and an efficiency of electric power reception of the power receiver 20B included in the electronic device 40B is 40%.

The efficiency of electric power reception of the power receivers 20A and 20B is expressed by a rate of electric power received the secondary-side coil 22 of each of the power receivers 20A and 20B, with respect to electric power transmitted from the primary-side coil 11 coupled to the AC power source 1. Note that in a case where the primary-side resonant coil 12 is directly coupled to the AC power source 1 and the power transmitter 10 does not include the primary-side coil 11, the received electric power may be calculated by using electric power transmitted from the primary-side resonant coil 12 instead of using the electric power transmitted from the primary-side coil 11. Further, in a case where the power receivers 20A and 20B do not include the secondary-side coil 22, received electric power may be calculated by using electric power received by the secondary-side resonant coil 21 instead of using the electric power received by the secondary-side coil 22.

The efficiency of electric power reception of the power receiver 20A and the efficiency of electric power reception of the power receiver 20B are determined depending on specifications of the coils of the power receivers 20A and 20B and of the power transmitter 10 and on distances/orientations between the power transmitter 10 and the respective power receivers 20A and 20B. In FIG. 2, because the power receivers 20A and 20B have the same configuration and are arranged at positions of equal distance/orientation from the power transmitter 10, the efficiency of electric power reception of the power receiver 20A and the efficiency of electric power reception of the power receiver 20B are equal to each other and, as an example, at 40%.

Further, a rated output of the electronic device 40A is taken as 10 W and a rated output of the electronic device 40B is taken as 5 W.

In such a case, electric power transmitted from the primary-side resonant coil 12 (see FIG. 1) of the power transmitter 10 is 18.75 W. Here, 18.75 W can be calculated by a formula of (10 W+5 W)/(40%+40%).

When electric power of 18.75 W is transmitted to the electronic devices 40A and 40B from the power transmitter 10, the power receivers 20A and 20B receive electric power of 15 W in total. Because the power receivers 20A and 20B equally receive the electric power, each of the power receivers 20A and 20B receives electric power of 7.5 W.

As a result, electric power to the electronic device 40A is insufficient by 2.5 W, and electric power to the electronic device 40B is excessive by 2.5 W.

That is, even when electric power of 18.75 W is transmitted from the power transmitter 10 to the electronic devices 40A and 40B, it is impossible to charge the electronic devices 40A and 40B in a balanced manner. In other words, when charging the electronic devices 40A and 40B simultaneously, the balance of supplying the electric power is not good.

FIG. 3 is a diagram illustrating a state where electric power is transmitted from the power transmitter 10 to electronic devices 40B1 and 40B2 through magnetic-field resonance.

The electronic devices 40B1 and 40B2 are the same type of smartphone and respectively include power receivers 20B1 and 20B2. Each of the power receivers 20B1 and 20B2 is equal to the power receiver 20B illustrated in FIG. 2. That is, each of the power receivers 20B1 and 20B2 includes the secondary-side resonant coil 21. Although a simplified power transmitter 10 is illustrated in FIG. 3, the power transmitter 10 is coupled to the AC power source 1 (see FIG. 1).

In FIG. 3, an angle (orientation) of the electronic device 40B1 with respect to the power transmitter 10 is equal to an angle (orientation) of the electronic device 40B2 with respect to the power transmitter 10. However, the electronic device 40B1 is arranged further away from the power transmitter 10 than the electronic device 40B2. The power receivers 20B1 and 20B2 included in the respective electronic devices 40B1 and 40B2 receive electric power from the power transmitter 10 through the magnetic field resonance in a non-contact state.

For example, in the state illustrated in FIG. 3, an efficiency of electric power reception of the power receiver 20B1 included in the electronic device 40B1 is 35%, and an efficiency of electric power reception of the power receiver 20B2 included in the electronic device 40B2 is 45%.

Here, because the angle (orientation) of the electronic device 40B1 with respect to the power transmitter 10 and the angle (orientation) of the electronic device 40B2 with respect to the power transmitter 10 are equal to each other, the efficiency of electric power reception of the power receiver 20B1 and the efficiency of electric power reception of the power receiver 20B2 are determined depending on distances between the power transmitter 10 and the respective power receivers 20B1 and 20B2. Thus, in FIG. 3, the efficiency of electric power reception of the power receiver 20B1 is lower than the efficiency of electric power reception of the power receiver 20B2. Note that both the rated output of the electronic device 40B1 and the rated output of the electronic device 40B2 are 5 W.

In such a case, electric power transmitted from the primary-side resonant coil 12 (see FIG. 1) of the power transmitter 10 is 12.5 W. Here, 12.5 W can be calculated by a formula of (5 W+5 W)/(35%+45%).

When electric power of 12.5 W is transmitted to the electronic devices 40B1 and 40B2 from the power transmitter 10, the power receivers 20B1 and 20B2 receive electric power of 10 W in total. Further, because the efficiency of electric power reception of the power receiver 20B1 is 35%, and the efficiency of electric power reception of the power receiver 20B2 is 45% in FIG. 3, the power receiver 20B1 receives electric power of about 4.4 W and the power receiver 20B2 receives electric power of about 5.6 W.

As a result, electric power to the electronic device 40B1 is insufficient by about 0.6 W, and electric power to the electronic device 40B2 is excessive by about 0.6 W.

That is, even when electric power of 12.5 W is transmitted from the power transmitter 10 to the electronic devices 40B1 and 40B2, it is impossible to charge the electronic devices 40B1 and 40B2 in a balanced manner. In other words, when charging the electronic devices 40B1 and 40B2 simultaneously, the balance of supplying the electric power is not good (has scope for improvement).

Here, in the above description of the supply balance of electric power, the angles (orientations) of the electronic devices 40B1 and 40B2 with respect to the power transmitter 10 are equal and the distances from the power transmitter 10 to the electronic devices 40B1 and 40B2 are different.

However, because the efficiencies of electric power reception are determined depending on the angles (orientations) and the distances between the power receivers 20B1 and 20B2 and the power transmitter 10, the efficiency of electric power reception of the power receiver 20B1 and the efficiency of electric power reception of the power receiver 20B2 become values different from the above described 35% and 45% when angles (orientations) of the electronic devices 40B1 and 40B2 are different from a positional relationship illustrated in FIG. 3.

The efficiency of electric power reception of the power receiver 20B1 and the efficiency of electric power reception of the power receiver 20B2 become different values from each other when angles (orientations) of the electronic devices 40B1 and 40B2, with respect to the power transmitter 10, are different even if the distances from the power transmitter 10 to the electronic devices 40B1 and 40B2 are equal to each other.

Next, a power transmitting system and a power receiver according to an embodiment will be described with reference to FIG. 4 and FIG. 5.

FIG. 4 is a diagram illustrating a power transmitting apparatus 80 and the power receiver 100 according to the embodiment. The power transmitting apparatus 80 includes an alternating-current (AC) power source 1 and a power transmitter 10. Although the AC power source 1 and the power transmitter 10 are equivalent to those illustrated in FIG. 1, FIG. 4 illustrates a more specific configuration.

The power transmitting apparatus 80 includes the AC power source 1 and the power transmitter 10.

The power transmitter 10 includes a primary-side coil 11, a primary-side resonant coil 12, a matching circuit 13, a capacitor 14, and a controller 15.

The power receiver 100 includes a secondary-side resonant coil 110, a rectifier circuit 120, a switch 130, a smoothing capacitor 140, a controller 150, and output terminals 160A and 160B. A DC-DC converter 210 is coupled to the output terminals 160A and 160B, and a battery 220 is coupled to an output side of the DC-DC converter 210.

First, the power transmitter 10 will be described. As illustrated in FIG. 4, the primary-side coil 11 is a loop-shaped coil, and is coupled to the AC power source 1 via the matching circuit 13 between two ends of the primary-side coil 11. The primary-side coil 11 is disposed close to but not in contact with the primary-side resonant coil 12. The primary-side coil 11 is electromagnetically coupled to the primary-side resonant coil 12. The primary-side coil 11 is disposed such that the central axis of the primary-side coil 11 matches the central axis of the primary-side resonant coil 12. The central axis of the primary-side coil 11 and the central axis of the primary-side resonant coil 12 are made to match each other in order to inhibit leakage of magnetic flux and to inhibit unnecessary generation of magnetic fields around the primary-side coil 11 and the primary-side resonant coil 12 as well as improving the coupling strength between the primary-side coil 11 and the primary-side resonant coil 12.

The primary-side coil 11 generates magnetic fields by alternating-current (AC) power supplied from the AC power source 1 via the matching circuit 13, and transmits the electric power to the primary-side resonant coil 12 by electromagnetic induction (mutual induction).

As illustrated in FIG. 4, the primary-side resonant coil 12 is disposed close to but not in contact with the primary-side coil 11. The primary-side resonant coil 12 is electromagnetically coupled to the primary-side coil 11. Further, the primary-side resonant coil 12 has a predetermined resonance frequency and is designed to have a very high Q factor. The resonance frequency of the primary-side resonant coil 12 is set to be equal to the resonance frequency of the secondary-side resonant coil 110. The capacitor 14 for adjusting the resonance frequency is coupled in series between the two ends of the primary-side resonant coil 12.

The resonance frequency of the primary-side resonant coil 12 is set to be identical to the frequency of the AC power that the AC power source 1 outputs. The resonance frequency of the primary-side resonant coil 12 is determined depending on a capacitance of the capacitor 14 and an inductance of the primary-side resonant coil 12. Hence, the capacitance of the capacitor 14 and the inductance of the primary-side resonant coil 12 are set such that the resonance frequency of the primary-side resonant coil 12 is identical to the frequency of the AC power output from the AC power source 1.

The matching circuit 13 is inserted for matching impedance of the primary-side coil 11 and that of the AC power source 1, and includes an inductor L and a capacitor C.

The AC power source 1 is a power source that outputs AC power having the frequency necessary for the magnetic field resonance, and includes an amplifier that amplifies the output power. The AC power source 1 may, for example, output high frequency AC power from several hundreds of kHz to several tens of MHz.

The capacitor 14 is a variable capacitance capacitor inserted in series between the two ends of the primary-side resonant coil 12. The capacitor 14 is disposed for adjusting the resonance frequency of the primary-side resonant coil 12. The electrostatic capacitance of the capacitor 14 is set by the controller 15.

The controller 15 controls the output frequency and the output voltage of the AC power source 1 and controls the electrostatic capacitance of the capacitor 14.

The power transmitting apparatus 80 as described above transmits, to the primary-side resonant coil 12 with magnetic induction, the AC power supplied from the AC power source 1 to the primary-side coil 11, and transmits the electric power from the primary-side resonant coil 12 to the secondary-side resonant coil 110 of the power receiver 100 through magnetic field resonance.

Next, the secondary-side resonant coil 110 included in the power receiver 100 will be described.

The secondary-side resonant coil 110 has a resonance frequency identical to that of the primary-side resonant coil 12, and is designed to have a very high Q factor. A pair of terminals of the secondary-side resonant coil 110 is coupled to the rectifier circuit 120.

The secondary-side resonant coil 110 outputs, to the rectifier circuit 120, the AC power transmitted from the primary-side resonant coil 12 of the power transmitter 10 through the magnetic field resonance.

The rectifier circuit 120 includes four diodes 121A to 121D. The diodes 121A to 121D are coupled in a bridge-like configuration, and rectify the full wave of the electric power input from the secondary-side coil 110 to output the full-wave rectified power.

The switch 130 is inserted in series on the high potential side line (upper side line in FIG. 4) of the pair of lines that couple the rectifier circuit 120 to the smoothing capacitor 140. For example, the switch 130 may be a switch that can perform transmission and cutoff of DC voltage at high speed such as a FET.

The electric power on which the full wave rectification is performed by the rectifier circuit 120 is input to the switch 130. Because the full-wave rectified power can be treated as direct-current power, the switch 130 may be a switch for direct-current. Because a switch having a simple structure such as a FET can be used for the switch 130 for direct-current, the switch 130 can be size-reduced. Here, as switches for alternating-current, there are switches using FETs, a relay, and a TRIAC. Because a relay is a mechanical switch, its size is large and there may be a durability issue in switching the relay at high speed. Also, a TRIAC is unsuitable for high speed switching such as 6.78 MHz. Also, because of including a plurality of FETs, the switch for alternating-current using the FETs is larger than the FET for direct-current, and effects that parasitic capacitance gives to alternating-current occur. Due to the above described reasons, there are advantages regarding use of FET for alternating-current as the switch 130 for size-reduction and for preventing the effects of parasitic capacitance.

Although details of a driving pattern of the switch 130 will be described later below, the switch 130 is driven by the controller 150 through Pulse Width Modulation (PWM). A duty cycle of the PWM drive pattern of the switch 130 is determined based on an efficiency of electric power reception of the secondary-side resonant coil 110 of the power receiver 100 and a rated output of a load circuit that receives electric power supplied from the power receiver 100. In FIG. 4, the load circuit is the battery 220.

Further, a frequency of the PWM drive pattern is set to be a frequency less than or equal to an alternating-current frequency at which the secondary-side resonant coil 110 receives electric power.

The smoothing capacitor 140 is coupled to the output side of the rectifier circuit 120, and smooths the electric power, on which the full-wave rectification is performed by the rectifier circuit 120, and outputs the smoothed power as direct-current power. The output terminals 160A and 160B are coupled to the output side of the smoothing capacitor 140. Because negative components of AC power are inverted into positive components, the electric power on which the full-wave rectification is performed by the rectifier circuit 120 can be treated as substantially AC power. However, stable DC power can be obtained by using the smoothing capacitor 140 even when ripple is included in the full wave rectified power.

The DC-DC converter 210 is coupled to the output terminals 160A and 160B, and converts the voltage of the direct-current power that is output from the power receiver 100 into the rated voltage of the battery 220 to output the converted voltage. The DC-DC converter 210 lowers the output voltage, of the rectifier circuit 120 to the rated voltage of the battery 220 in a case where the output voltage of the rectifier circuit 120 is higher than the rated voltage of the battery 220. Further, the DC-DC converter 210 raises the output voltage, of the rectifier circuit 120 to the rated voltage of the battery 220 in a case where the output voltage of the rectifier circuit 120 is lower than the rated voltage of the battery 220.

The battery 220 may be any rechargeable secondary battery that can be repeatedly charged. For example, a lithium ion battery may be used as the battery 220. For example, in a case where the power receiver 100 is included in an electronic device such as a tablet computer or a smartphone, the battery 220 is a main battery of the electronic device.

For example, the primary-side coil 11, the primary-side resonant coil 12, and the secondary-side resonant coil 110 may be made by winding cooper wires. However, materials of the primary-side coil 11, the primary-side resonant coil 12, and the secondary-side resonant coil 110 may be metal other than copper (e.g., gold, aluminum, etc.). Further, materials of the primary-side coil 11, the primary-side resonant coil 12, and the secondary-side resonant coil 110 may be different from one another.

In such a configuration, the primary-side coil 11 and the primary-side resonant coil 12 correspond to a power transmitting side, and the secondary-side resonant coil 110 corresponds to a power receiving side.

According to a magnetic field resonance system, magnetic field resonance, generated between the primary-side resonant coil 12 and the secondary-side resonant coil 110, is utilized to transmit electric power from the power transmitting side to the power receiving side. Hence, it is possible to transmit the electric power over a longer distance than that of the electromagnetic induction system that utilizes electromagnetic induction to transmit electric power from the power transmitting side to the power receiving side.

The magnetic field resonance system is more flexible than the electromagnetic induction system with respect to the position gap or the distance between the resonant coils. The magnetic field resonance system thus has an advantage called “free-positioning”.

FIG. 5 is a diagram illustrating electronic devices 200A and 200B and the power transmitting apparatus 80 using a power transmitting system 500 according to the embodiment.

Although the power transmitting apparatus 80 in FIG. 5 is the same as the power transmitting apparatus 80 illustrated in FIG. 4, configuration elements other than the primary-side coil 11 and the controller 15 in FIG. 4 are expressed as a power source part 10A. The power source part 10A expresses the primary-side resonant coil 12, the matching circuit 13, and the capacitor 14 collectively. Note that the AC power source 1, the primary-side resonant coil 12, the matching circuit 13, and the capacitor 14 may be treated as the power source part collectively.

The power transmitting apparatus 80 further includes an antenna 16. For example, the antenna 16 may be any antenna that can perform wireless communication in a short distance such as Bluetooth (registered trade mark). The antenna 16 is provided in order to receive, from the power receivers 100A and 100B included in the electronic devices 200A and 200B, data representing the efficiency of electric power reception and the rated output. The received data is input to the controller 15. The controller 15 is an example of a controller and, is an example of a third communication part.

Each of the electronic devices 200A and 200B may be a terminal device such as a tablet computer or a smartphone, for example. The electronic devices 200A and 200B respectively include the power receivers 100A and 100B, DC-DC converters 210A and 210B, and the batteries 220A and 220B.

The power receivers 100A and 100B respectively have configurations where antennas 170A and 170B are added to the power receiver 100 illustrated in FIG. 4. Each of the DC-DC converters 210A and 210B is equivalent to the DC-DC converter 210 illustrated in FIG. 4. Further, each of the batteries 220A and 220B is equivalent to the battery 220 illustrated in FIG. 4.

The power receiver 100A includes a secondary-side resonant coil 110A, a rectifier circuit 120A, a switch 130A, a smoothing capacitor 140A, a controller 150A, and the antenna 170A. The secondary-side resonant coil 110A, the rectifier circuit 120A, the switch 130A, the smoothing capacitor 140A, and the controller 150A respectively correspond to the secondary-side resonant coil 110, the rectifier circuit 120, the switch 130, the smoothing capacitor 140, and the controller 150 illustrated in FIG. 4. Note that, in FIG. 5, the secondary-side resonant coil 110A, the rectifier circuit 120A, the switch 130A, and the smoothing capacitor 140A are illustrated in a simplified manner, and the output terminals 160A and 160B are omitted.

The power receiver 100B includes a secondary-side resonant coil 110B, a rectifier circuit 120B, a switch 130B, a smoothing capacitor 140B, a controller 150B, and the antenna 170B. The secondary-side resonant coil 110B, the rectifier circuit 120B, the switch 130B, the smoothing capacitor 140B, and the controller 150B respectively correspond to the secondary-side resonant coil 110, the rectifier circuit 120, the switch 130, the smoothing capacitor 140, and the controller 150 illustrated in FIG. 4. Note that, in FIG. 5, the secondary-side resonant coil 110B, the rectifier circuit 120B, the switch 130B, and the smoothing capacitor 140B are illustrated in a simplified manner, and the output terminals 160A and 160B are omitted.

For example, the antennas 170A and 170B may be any antenna that can perform wireless communication in a short distance such as Bluetooth (registered trade mark). The antennas 170A and 170B are provided in order to perform data communication with the antenna 16 of the power transmitter 10. The antennas 170A and 170B are coupled to the controllers 150A and 150B of the power receivers 100A and 100B, respectively. The controllers 150A and 150B are examples of a drive controller. The controllers 150A and 150B are examples of a first communication part and a second communication part, respectively.

The controller 150A of the power receiver 100A transmits, to the power transmitter 10 via the antenna 170A, data representing an efficiency of electric power reception of the secondary-side resonant coil 110A and a rated output of the battery 220A. Similarly, the controller 150B of the power receiver 100B transmits, to the power transmitter 10 via the antenna 170B, data representing an efficiency of electric power reception of the secondary-side resonant coil 110B and a rated output of the battery 220B.

In a state where the electronic devices 200A and 200B are arranged close to the power transmitting apparatus 80, the electronic devices 200A and 200B can respectively charge the batteries 220A and 220B without contacting the power transmitting apparatus 80. The batteries 220A and 220B can be charged at the same time.

The power transmitting system 500 is structured with the power transmitter 10 and the power receivers 100A and 100B of the configuration elements illustrated in FIG. 5. That is, the power transmitting apparatus 80 and the electronic devices 200A and 200B adopt the power transmitting system 500 that enables power transmission in a non-contact state through the magnetic field resonance.

Here, when the batteries 220A and 220B are charged at the same time, a state may occur in which the balance of electric power supplied to the electronic devices 200A and 200B is not good as described with reference to FIG. 2 and FIG. 3.

Hence, in order to improve the balance of supplied electric power, the power receivers 100A and 100B set duty cycles of PWM drive patterns that drive the switches 130A and 130B based on the efficiency of electric power reception of the secondary-side resonant coil 110A, the rated output of the battery 220A, the efficiency of electric power reception of the secondary-side resonant coil 110B, and the rated output of the battery 220B.

FIG. 6 is a diagram illustrating a relationship between duty cycles of PWM drive patterns and amounts of received electric power of the power receivers 100A and 100B.

Here, a case, in which the duty cycle of the PWM drive pattern that drives the switch 130B of the power receiver 100B is decreased from 100% with respect to a state in which the duty cycle of the PWM drive pattern that drives the switch 130A of the power receiver 100A is fixed to 100%, will be described.

In FIG. 6, a horizontal axis indicates the duty cycle of the PWM drive pattern that drives the switch 130B of the power receiver 100B. Further, a left side vertical axis indicates proportions of the efficiencies of electric power reception of the power receivers 100A and 100B. Further, a right side vertical axis indicates, in percentage, a sum of the efficiencies of electric power reception of the power receivers 100A and 100B.

Here, the proportions of the efficiencies of electric power reception are proportions of the respective efficiencies of electric power reception of the power receivers 100A and 100B to the sum of the efficiencies of electric power reception, when the sum of the efficiencies of electric power reception of the power receivers 100A and 100B is taken as 100%. For example, in a case where both the efficiency of electric power reception of the power receiver 100A and the efficiency of electric power reception of the power receiver 100B are equal to each other and are 40% (sum of the efficiencies of electric power reception is 80%), both the proportion of the efficiency of electric power reception of the power receiver 100A and the proportion of the efficiency of electric power reception of the power receiver 100B are 50%.

The case, in which both the efficiency of electric power reception of the power receiver 100A and the efficiency of electric power reception of the power receiver 100B are equal to each other and are 40%, means a state in which both the efficiency of electric power reception of the power receiver 100A and the efficiency of electric power reception of the power receiver 100B are equal to each other and are 40% when the two power receivers 100A and 100B simultaneously receive electric power from the power transmitter 10. Note that each of the power receivers 100A and 100B has the efficiency of electric power reception of about 85% singly.

Here, for example, it is assumed that, in a state in which both the duty cycle of the PWM drive pattern that drives 130A of the power receiver 100A and the duty cycle of the PWM drive pattern that drives 130B of the power receiver 100B are 100%, both the proportion of the efficiency of electric power reception of the power receiver 100A and the proportion of the efficiency of electric power reception of the power receiver 100B are 50%.

When the duty cycle of the PWM drive pattern that drives the switch 130B of the power receiver 100B is decreased from 100%, in the state in which the duty cycle of the PWM drive pattern that drives the switch 130A of the power receiver 100A is fixed to 100%, the proportion of the efficiency of electric power reception of the power receiver 100B decreases as illustrated in FIG. 6. Further, in accordance with this, the proportion of the efficiency of electric power reception of the power receiver 100A increases.

In this way, when the duty cycle of the PWM drive pattern that drives the switch 130B of the power receiver 100B is decreased, electric current that flows through the power receiver 100B decreases because the amount of received electric power of the power receiver 100B decreases. That is, the impedance of the power receiver 100B is changed depending on the change of the duty cycle.

In electric power transmission using magnetic field resonance, electric power, transmitted from the power transmitter 10 to the power receivers 100A and 100B through the magnetic field resonance, is distributed to the power receivers 100A and 100B. Hence, when the duty cycle of the PWM drive pattern that drives the switch 130B of the power receiver 100B is decreased from 100%, the amount of received electric power of the power receiver 100A increases by the decrease in the amount of received electric power of the power receiver 100B.

Hence, as illustrated in FIG. 6, the proportion of the efficiency of electric power reception of the power receiver 100B decreases. Further, in accordance with this, the proportion of the efficiency of electric power reception of the power receiver 100A increases.

When the duty cycle of the PWM drive pattern that drives the switch 130B of the power receiver 100B decreases to about 10%, the proportion of the efficiency of electric power reception of the power receiver 100B decreases to about 13% and the proportion of the efficiency of electric power reception of the power receiver 100A increases to about 87%.

Then, when the duty cycle of the PWM drive pattern that drives the switch 130B of the power receiver 100B is 100%, the sum of the efficiencies of electric power reception of the power receiver 100A and the power receiver 100B is about 85%. When the duty cycle of the PWM drive pattern that drives the switch 130B of the power receiver 100B is decreased to about 10%, the sum of the efficiencies of electric power reception of the power receiver 100A and the power receiver 100B becomes about 70%.

As described above, when the duty cycle of the PWM drive pattern for driving the switch 130B of the power receiver 100B is decreased from 100% in the state in which the duty cycle of the PWM drive pattern for driving the switch 130A of the power receiver 100A is fixed to 100%, the proportion of the efficiency of electric power reception of the power receiver 100B decreases and the proportion of the efficiency of electric power reception of the power receiver 100A increases. Then, the sum of the efficiency of electric power reception of the power receiver 100A and the efficiency of electric power reception of the power receiver 100B is a value around 80%, and does not largely change.

In electric power transmission using magnetic field resonance, the sum of the efficiencies of electric power reception of the power receivers 100A and 100B does not largely change even when the duty cycle is changed because electric power, transmitted from the power transmitter 10 to the power receivers 100A and 100B through the magnetic field resonance, is distributed to the power receivers 100A and 100B.

Similarly, when the duty cycle of the PWM drive pattern for driving the switch 130A of the power receiver 100A is decreased from 100% in a state in which the duty cycle of the PWM drive pattern for driving the switch 130B of the power receiver 100B is fixed to 100%, the proportion of the efficiency of electric power reception of the power receiver 100A decreases and the proportion of the efficiency of electric power reception of the power receiver 100B increases. Then, the sum of the efficiency of electric power reception of the power receiver 100A and the efficiency of electric power reception of the power receiver 100B is a value around 80%, and does not largely change.

Accordingly, it is possible to adjust the proportion of the efficiency of electric power reception of the power receiver 100A and the proportion of the efficiency of electric power reception of the power receiver 100B by adjusting the duty cycle of the PWM drive pattern that drives either the switch 130A of the power receiver 100A or the switch 130B of the power receiver 100B.

As described above, when the duty cycle of the PWM drive pattern that drives the switch 130A or the switch 130B is changed, the proportions of the efficiencies of electric power reception of the secondary-side resonant coils 110A and 110B of the power receivers 100A and the power receiver 100B are changed.

Hence, according to the embodiment, the duty cycle of one PWM drive pattern of the PWM drive patterns for the switches 130A and 130B of the power receivers 100A and 100B is changed from a standard duty cycle. For example, the standard duty cycle may be 100%, and in this case, the one duty cycle is set to be an appropriate value less than 100%.

At this time, determination, as to whether to change the duty cycle of the PWM drive pattern of the switch 130A from the standard duty cycle or to change the duty cycle of the PWM drive pattern of the switch 130B from the standard duty cycle, is made as follows.

First, a first value, obtained by dividing the rated output of the battery 220A by the efficiency of electric power reception of the secondary-side resonant coil 110A and a second value, obtained by dividing the rated output of the battery 220B by the efficiency of electric power reception of the secondary-side resonant coil 110B, are calculated.

Then, the duty cycle of the PWM drive pattern corresponding to the power receiver (100A or 100B), having the smaller value of the first value and the second value, is set to be an appropriate value less than duty cycle 100%.

The value, obtained by dividing the rated output by the efficiency of electric power reception, represents an amount of electric power (required amount of transmission electric power) that the power transmitter 10 transmits to the power receiver 100A or 100B. The required amount of transmission electric power is an amount of electric power that is transmitted from the power transmitter 10 so that the power receiver (100A or 100B) receives the electric power without generating excessive electric power and insufficient electric power.

Accordingly, by reducing an amount of electric power supplied to the power receiver (100A or 100B) of which the required amount of transmission electric power is smaller, it is possible to increase an amount of electric power supplied to the power receiver (100A or 100B) of which the required amount of transmission electric power is larger. As a result, it is possible to improve the balance between the amount of electric power supplied to the power receiver 100A and the amount of electric power supplied to the power receiver 100B.

As can be seen from FIG. 6, when the duty cycle of one power receiver (100A or 100B) is decreased, the amount of received electric power of the one power receiver (100A or 100B) decreases. Further, the amount of received electric power of the other power receiver (100A or 100B) increases in a state in which the duty cycle of the other power receiver (100A or 100B) is fixed.

Hence, by decreasing the duty cycle of the PWM drive pattern corresponding to the power receiver (100A or 100B) of which the required amount of transmission electric power is smaller, it is possible to reduce the amount of electric power supplied to the power receiver (100A or 100B) of which the required amount of transmission electric power is smaller and to increase the amount of electric power supplied to the power receiver (100A or 100B) of which the required amount of transmission electric power is larger.

In this way, the balance of the amounts of electric power supplied to the power receivers 100A and 100B may be improved. Note that a method for setting a specific duty cycle will be described later below.

Further, at this time, the frequency of the PWM drive pattern is set to be a frequency less than or equal to a frequency of AC power that is transmitted through the magnetic field resonance. More preferably, the frequency of the PWM drive pattern is set to be a frequency less than the frequency of the AC power that is transmitted through the magnetic field resonance. For example, the frequency of the PWM drive pattern may be set to be a frequency less than the frequency of the AC power, which is transmitted through the magnetic field resonance, by about one or two orders of magnitude.

This is because if the frequency of the PWM drive pattern is higher than the frequency of the AC power that is transmitted through the magnetic field resonance, ON/OFF of the switch 130A or 130B is switched in the process of one cycle of full wave rectified electric power and there is a possibility that it becomes impossible to appropriately adjust the amount of electric power.

Accordingly, it is required to set the frequency of the PWM drive pattern to be a frequency less than or equal to the frequency of the AC power that is transmitted through the magnetic field resonance. Further, at that time, by setting the frequency of the PWM drive pattern to a frequency less than the frequency of the AC power, which is transmitted through the magnetic field resonance, by about one or two orders of magnitude, it becomes possible to appropriately adjust the amount of electric power.

For example, in a case where the frequency of the AC power that is transmitted through the magnetic field resonance is 6.78 MHz, the frequency of the PWM drive pattern may be set to be several hundreds of KHz.

Here, a relationship between the duty cycle of the PWM drive pattern and the received electric power will be described with reference to FIG. 7.

FIG. 7 is a diagram illustrating a relationship between the duty cycle of the PWM drive pattern and the received electric power in the power receiver 100.

In FIG. 7, the secondary-side resonant coil 110, the rectifier circuit 120, the switch 130, and the smoothing capacitor 140 of the power receiver 100 are illustrated in a simplified manner, and electric power waveforms (1), (2), and (3) are illustrated.

The electric power waveform (1) represents a waveform of electric power that is obtained between the secondary-side resonant coil 110 and the rectifier circuit 120. The electric power waveform (2) represents a waveform of electric power that is obtained between the rectifier circuit 120 and the switch 130. The electric power waveform (3) represents a waveform of electric power that is obtained between the switch 130 and the smoothing capacitor 140.

Here, because the electric power waveform in the input side of the switch 130 is substantially equal to the electric power waveform in the output side of the switch 130, the electric power waveform (2) is also an electric power waveform that is obtained between the switch 130 and the smoothing capacitor 140.

Here, it is assumed that the frequency of AC voltage that the AC power source 1 outputs is 6.78 MHz and the resonance frequency of the primary-side resonant coil 12 and the secondary-side resonant coil 21 is 6.78 MHz. Further, it is assumed that the frequency of the PWM pulse of the PWM drive pattern is 300 kHz and the duty cycle is 50%.

As illustrated in FIG. 4, the power receiver 100 has a circuit configuration, which forms a loop between the secondary-side resonant coil 110 and the battery 220, in practice.

Hence, electric current flows through the loop circuit while the switch 130 is turned on, but electric current does not flow through the loop circuit while the switch 130 is turned off.

The electric power waveform (1) is a waveform of the AC power, which is supplied from the secondary-side resonant coil 110 to the rectifier circuit 120, intermittently flowing in accordance with ON/OFF of the switch 130.

The electric power waveform (2) is a waveform of the electric power, full wave rectified by the rectifier circuit 120, intermittently flowing in accordance with ON/OFF of the switch 130.

The electric power waveform (3) is DC power obtained by smoothing the electric power, full wave rectified by the rectifier circuit 120 and supplied to the smoothing capacitor 140 via the switch 130. A voltage value of the electric power waveform (3) increases as the duty cycle increases, and decreases as the duty cycle decreases.

As described above, the voltage value of the DC power that is output from the smoothing capacitor 140 can be adjusted by adjusting the duty cycle of the drive pattern.

Next, a method of setting the duty cycle will be described.

When the duty cycle of the PWM drive pattern is changed in a case where electric power transmission of the magnetic field resonance type is performed, a degree of change of the efficiency of electric power reception does not change linearly with respect to a degree of change of the duty cycle.

For example, it is assumed that both the efficiency of electric power reception of the secondary-side resonant coil 110A and the efficiency of electric power reception of the secondary-side resonant coil 110B are 40% in a case where the duty cycles of the PWM drive patterns corresponding to the power receivers 100A and 100B are 100%.

In this case, when the duty cycle of the PWM drive pattern corresponding to the power receiver 100B is decreased to 71% in a state in which the duty cycle of the PWM drive pattern corresponding to the power receiver 100A is maintained at 100%, the efficiency of electric power reception of the secondary-side resonant coil 110A and the efficiency of electric power reception of the secondary-side resonant coil 110B become 50% and 25%, respectively.

As described above, because there is a non-linear relationship between the degree of change of the duty cycle of the PWM drive pattern and the degree of change of the efficiency of electric power reception, table data that associates duty cycles with efficiencies of electric power reception may be created and a duty cycle for obtaining a desired efficiency of electric power reception may be selected.

Next, a method, by which the power transmitter 10 obtains data that represents an efficiency of electric power reception and a rated output from each of the power receivers 100A and 100B, will be described with reference to FIG. 8.

FIG. 8 is a task diagram illustrating processing that the power transmitter 10 and the power receivers 100A and 100B execute for setting the duty cycles. This task is executed by the controllers 15, 150A and 150B (see FIG. 5).

First, the power receiver 100A transmits data, which represents received electric power, to the power transmitter 10 in step S1A. Similarly, the power receiver 100B transmits data, which represents received electric power, to the power transmitter 10 in step S1B. In this way, the power transmitter 10 receives the data representing the received electric power from each of the power receivers 100A and 100B.

For example, in response to a request from the power transmitter 10, the controllers 150A and 150B transmits the data, which represents the received electric power, via the antennas 170A and 170B. Further, the data representing the received electric power may include an identifier for identifying the power receivers 100A and 100B.

The data representing the received electric power may be obtained as follows. First, a signal for setting the duty cycle to be 0% is transmitted from the power transmitter 10 to the power receiver 100B through wireless communication and a signal for setting the duty cycle to be 100% is transmitted from the power transmitter 10 to the power receiver 100A through wireless communication.

Then, predetermined electric power is transmitted from the power transmitter 10 to the power receiver 100A through magnetic field resonance, and the power receiver 100A receives the electric power. At this time, when a signal, which represents the amount of electric power received by the power receiver 100A, is transmitted to the power transmitter 10, the power transmitter 10 can measure the efficiency of electric power reception of the power receiver 100A. Note that, at this time, the power receiver 100B is in an OFF state (non-operating state) because the duty cycle is 0%.

When measuring the efficiency of electric power reception of the power receiver 100B, a signal for setting the duty cycle to be 0% is transmitted from the power transmitter 10 to the power receiver 100A through wireless communication and a signal for setting the duty cycle to be 100% is transmitted from the power transmitter 10 to the power receiver 100B through wireless communication. When predetermined electric power is transmitted from the power transmitter 10 to the power receiver 100B through magnetic field resonance and a signal, which represents the amount of electric power received by the power receiver 100B, is transmitted to the power transmitter 10, the power transmitter 10 can measure the efficiency of electric power reception of the power receiver 100B.

Next, the power receiver 100A transmits data, which represents the rated output, to the power transmitter 10 in step S2A. Similarly, the power receiver 100B transmits data, which represents the rated output, to the power transmitter 10 in step S2B. In this way, the power transmitter 10 receives the data representing the rated output from each of the power receivers 100A and 100B in step S2.

For example, the data representing the rated output of the electronic device 200A may be previously stored in an internal memory of the controller 150A and the data representing the rated output of the electronic device 200B may be previously stored in an internal memory of the controller 150B. Then, the controllers 150A and 150B may transmit the stored data via the antennas 170A and 170B after transmitting the data representing the efficiency of electric power reception.

Next, the power transmitter 10 calculates, based on the data representing the efficiency of electric power reception of the power receiver 100A, the data representing the rated output of the power receiver 100A, the data representing the efficiency of electric power reception of the power receiver 100B, and on the data representing the rated output of the power receiver 100B, duty cycles of the PWM drive patterns corresponding to the power receivers 100A and 100B in step S3. One of the duty cycles is a standard duty cycle (100%), and the other of the duty cycles is an optimized duty cycle that is less than 100%. Details of step S3 will be described later below with reference to FIG. 12.

Next, the power transmitter 10 transmits the data representing the duty cycle to each of the power receivers 100A and 100B in step S4. Then, the power receiver 100A receives the duty cycle in step S4A and the power receiver 100B receives the duty cycle in step S4B.

Here, the controller 15 of the power transmitter 10 is set to transmit, to the power receivers 100A and 100B via the antenna 16, the data representing the duty cycle after calculating the duty cycle.

The controller 150A of the power receiver 100A sets the duty cycle for the PWM drive pattern in step S5A and the controller 150B of the power receiver 100B sets the duty cycle for the PWM drive pattern in step S5B.

The power transmitter 10 starts to transmit electric power in step S6. For example, the process of step S6 is executed when it is reported to the power transmitter 10 that the controller 150A and 150B complete the setting of the duty cycle to the PWM drive pattern.

Here, a method of obtaining the data representing the efficiencies of electric power reception of the power receivers 100A and 100B will be described with reference to FIG. 9 and FIG. 10.

FIG. 9 is a diagram illustrating equivalent circuits of the power transmitting apparatus 80 and the electronic devices 200A and 200B. The equivalent circuits illustrated in FIG. 9 corresponds to the power transmitting apparatus 80 and the electronic devices 200A and 200B illustrated in FIG. 5. However, in the following description, the power transmitting apparatus 80 does not include a primary-side coil 11, and the primary-side resonant coil 12 is directly coupled to the AC power source 1.

In FIG. 9, the secondary-side resonant coil 110A is a coil L_(RA) and a resistor R_(RA), the smoothing capacitor 140A is a capacitor C_(SA), and the DC-DC converter 210A and the battery 220A are a resistor R_(LA).

Similarly, the secondary-side resonant coil 110B is a coil L_(RB) and a resistor R_(RB), the smoothing capacitor 140B is a capacitor C_(SB), and the DC-DC converter 210B and the battery 220B are a resistor R_(LB).

Further, the resonant coil 12 of the power transmitting apparatus 80 is a resistor R_(T) and a coil L_(T), and the AC power source 1 is a power source V_(S) and a resistor R_(S).

A mutual inductance between the power transmitting apparatus 80 and the electronic device 200A is M_(TA), a mutual inductance between the power transmitting apparatus 80 and the electronic device 200B is M_(TB), and a mutual inductance between the electronic device 200A and the electronic device 200B is M_(AB).

Here, because the mutual inductance M_(AB) is negligibly smaller in comparison with the mutual inductance M_(TA) and the mutual inductance M_(TB), the mutual inductance M_(TA) and the mutual inductance M_(TB) are discussed here.

The mutual inductance M_(TA) is determined depending on the efficiency of electric power reception of the power receiver 100A of the electronic device 200A with the power transmitting apparatus 80. This is because the efficiency of electric power reception is determined depending on a position (distance) and an orientation (angle) of the power receiver 100A with respect to the power transmitting apparatus 80. Similarly, the mutual inductance M_(TB) is determined depending on the efficiency of electric power reception of the power receiver 100B of the electronic device 200B with the power transmitting apparatus 80.

The efficiency of electric power reception of the power receiver 100A can be calculated by transmitting electric power from the power transmitter 10 to the power receiver 100A and measuring an amount of electric power received by the power receiver 100A in a state of turning off the power receiver 100B. Similarly, the efficiency of electric power reception of the power receiver 100B can be calculated by transmitting electric power from the power transmitter 10 to the power receiver 100B and measuring an amount of electric power received by the power receiver 100B in a state of turning off the power receiver 100A.

Accordingly, the mutual inductance M_(TA) and the mutual inductance M_(TB) can be obtained by obtaining the efficiency of electric power reception of the power receiver 100A alone and the efficiency of electric power reception of the power receiver 100B alone.

According to the embodiment, the duty cycle of the PWM drive pattern that drives the switch 130A or the switch 130B is changed in order to change the proportions of the efficiencies of electric power reception of the secondary-side resonant coils 110A and 110B of the power receivers 100A and 100B.

Hence, table data is prepared in advance that associates duty cycles with relationships between mutual inductances M_(TA) and mutual inductances M_(TB). Then, the duty cycle of the PWM drive pattern is adjusted by using such table data.

FIGS. 10A and 10B are diagrams illustrating table data that associates duty cycles with relationships between mutual inductances M_(TA) and mutual inductances M_(TB).

FIG. 10A is table data for adjusting the duty cycle of the PWM drive pattern that drives the switch 130A in the state in which the duty cycle of the PWM drive pattern that drives the switch 130B is fixed to 100%.

Mutual inductances M_(TA) 1, M_(TA) 2, M_(TA) 3, . . . have specific values of mutual inductance M_(TA) in practice. Similarly, mutual inductances M_(TB) 1, M_(TB) 2, M_(TB) 3, . . . have specific values of mutual inductance M_(TB) in practice. Duty cycles duty 1A, duty 2A, duty 3A, . . . duty 11A, duty 12A, duty 13A, . . . have specific values of duty cycle experimentally obtained.

FIG. 10B is table data for adjusting the duty cycle of the PWM drive pattern that drives the switch 130B in the state in which the duty cycle of the PWM drive pattern that drives the switch 130A is fixed to 100%.

Mutual inductances M_(TA) 1, M_(TA) 2, M_(TA) 3, . . . and mutual inductances M_(TB) 1, M_(TB) 2, M_(TB)3, . . . are similar to those of FIG. 10A. Duty cycles duty 1B, duty 2B, duty 3B, . . . duty 11B, duty 12B, duty 13B, . . . have specific values of duty cycle experimentally obtained.

The table data illustrated in FIGS. 10A and 10B can be created by trying to optimize the duty cycle with measuring the mutual inductances M_(TA) and M_(TB) while positions and orientations of the power receivers 100A and 100B with respect to the power transmitter 10 are variously changed.

FIGS. 11A and 11B are diagrams illustrating table data that associates efficiencies of electric power reception with mutual inductances M_(TA) and M_(TB). FIG. 11A is table data that associates respective mutual inductances M_(TA) with efficiencies of electric power reception of the power receiver 100A. FIG. 11B is table data that associates respective mutual inductances M_(TB) with efficiencies of electric power reception of the power receiver 100B.

The mutual inductances M_(TA) and M_(TB) are respectively determined depending on the efficiencies of electric power reception between the power transmitting apparatus 80 and the power receivers 100A and 100B.

In FIG. 11A, the mutual inductances M_(TA) 1, M_(TA)2, . . . are associated with the efficiencies E_(A) 1, E_(A)2, . . . of electric power reception of the power receiver 100A. Also, in FIG. 11B, the mutual inductances M_(TB) 1, M_(TB)2, . . . are associated with the efficiencies E_(B) 1, E_(B) 2, . . . of electric power reception of the power receiver 100B.

By previously measuring the efficiencies of electric power reception and the mutual inductances M_(TA) and M_(TB) of the power receivers 100A and 100B through experiments or the like to create table data as illustrated in FIGS. 11A and 11B, the mutual inductances M_(TA) and M_(TB) can be obtained from the efficiencies of electric power reception of the power receivers 100A and 100B. Alternatively, the mutual inductances M_(TA) and M_(TB) can be obtained through a simulation.

Next, a method of setting the duty cycle will be described with reference to FIG. 12.

FIG. 12 is a flowchart illustrating a method by which the power transmitter 10 sets the duty cycle of the power receiver 100A or 100B according to the embodiment. This flow illustrates processing that is executed by the controller 15 of the power transmitter 10 and illustrates details of the process of step S3 of FIG. 8.

The controller 15 starts processing illustrated in FIG. 12, upon proceeding to step S3 by receiving from the power receivers 100A and 100B the signals that represent the received electric power to obtain the efficiencies of electric power reception and receiving from the power receivers 100A and 100B the signals that represent the rated outputs.

The controller 15 calculates a first value, obtained by dividing the rated output of the battery 220A by the efficiency of electric power reception of the secondary-side resonant coil 110A and a second value, obtained by dividing the rated output of the battery 220B by the efficiency of electric power reception of the secondary-side resonant coil 110B, and determines whether the first value is greater than the second value in step S31.

Upon determining that the first value is greater than the second value (YES in step S31), the controller 15 sets the duty cycle of the PWM drive pattern that drives the switch 130A of the power receiver 100A to be 100% in step S32A.

Next, the controller 15 sets the duty cycle of the PWM drive pattern that drives the switch 130B of the power receiver 100B in step S32A. Specifically, based on the table data illustrated in FIGS. 11A and 11B, the controller 15 obtains the mutual inductances M_(TA) and M_(TB) of the power receivers 100A and 100B from the efficiencies E_(A) and E_(B) of electric power reception of the power receivers 100A and 100B respectively. Then, from the table data illustrated in FIG. 10B, the controller 15 obtains the duty cycle of the PWM drive pattern that drives the switch 130B of the power receiver 100B based on the mutual inductances M_(TA) and M_(TB) of the power receivers 100A and 100B.

When the process of step S32A is finished, the controller 15 causes the flow to proceed to step S4 (see FIG. 8).

Upon determining that the first value is less than the second value (NO in step S31), the controller 15 sets the duty cycle of the PWM drive pattern that drives the switch 130B of the power receiver 100B to be 100% in step S32B.

Next, the controller 15 sets the duty cycle of the PWM drive pattern that drives the switch 130A of the power receiver 100A in step S32B. Specifically, based on the table data illustrated in FIGS. 11A and 11B, the controller 15 obtains the mutual inductances M_(TA) and M_(TB) of the power receivers 100A and 100B from the efficiencies E_(A) and E_(B) of electric power reception of the power receivers 100A and 100B respectively. Then, from the table data illustrated in FIG. 10A, the controller 15 obtains the duty cycle of the PWM drive pattern that drives the switch 130A of the power receiver 100A based on the mutual inductances M_(TA) and M_(TB) of the power receivers 100A and 100B.

When the process of step S32B is finished, the controller 15 causes the flow to proceed to step S4 (see FIG. 8).

In this way, the controller 15 sets the duty cycles of the PWM drive patterns for driving the switches 130A and 130B of the power receivers 100A and 100B.

As described above, according to the embodiment, the required amount of electric power transmitted to the power receiver 100A and the required amount of electric power transmitted to the power receiver 100B are obtained by the efficiencies of electric power reception of the secondary-side resonant coils 110A and 110B of the power receivers 100A and 100B and the rated outputs of the electronic devices 200A and 200B.

Then, the duty cycle of the PWM drive pattern corresponding to the power receiver (100A or 100B) of which the required amount of transmission electric power is smaller among the power receivers 100A and 100B is decreased.

As a result, by reducing the duty cycle of the PWM drive pattern corresponding to the power receiver (100A or 100B) of which the required amount of transmission electric power is smaller, the amount of electric power supplied to the power receiver (100A or 100B) of which the required amount of transmission electric power is smaller is reduced and it is possible to increase the amount of electric power supplied to the power receiver (100A or 100B) of which the required amount of transmission electric power is larger.

In this way, the balance between the amount of electric power supplied to the power receiver 100A and the amount of electric power supplied to the power receiver 100B is improved.

Thus, according to the embodiment, it is possible to provide the power receiver 100A or 100B that can improve the balance of supplied amounts of electric power. Further, according to the embodiment, it is possible to provide the power transmitting system 500 that can improve the balance of supply amounts of electric power.

Note that in the above described embodiment, the switch 130 is directly coupled to the output side of the rectifier circuit 120. However, a power receiver 101 having a circuit configuration as illustrated in FIG. 13 may be used.

FIG. 13 is a diagram illustrating the power receiver 101 according to a variation example of the embodiment. The power receiver 101 has a configuration in which a smoothing capacitor 170 is added between the rectifier circuit 120 and the switch 130 in the power receiver 100 illustrated in FIG. 4. With this, electric power, on which the full wave rectification is performed by the rectifier circuit 120, can be input to the switch 130 after being smoothed. Therefore, if effects of ripple included in the full wave rectified power occur, the effects of the ripple are effectively prevented, for example.

Further, in the above description of the embodiment, the balance between the amount of electric power supplied to the power receiver 100A and the amount of electric power supplied to the power receiver 100 is improved by decreasing the duty cycle of the PWM drive pattern corresponding to the power receiver (100A or 100B) of which the required amount of transmission electric power is smaller among the power receivers 100A and 100B.

However, there may be a case where three or more power receivers are charged at the same time. In such a case, a duty cycle of a PWM drive pattern of a power receiver other than a power receiver of which the required amount of electric power is largest, among amounts of electric power obtained by dividing respective rated outputs by efficiencies of electric power reception, may be decreased.

Further, in the above description of the example of the embodiment, each of the electronic devices 200A and 200B is a terminal device such as a tablet computer or a smartphone. However, each of the electronic devices 200A and 200B may be an electronic device that includes a chargeable battery such as a node-type Personal Computer (PC), a portable phone terminal, a portable game machine, a digital camera, or a video camera, for example.

Although examples of the power receivers and the power transmitting system according to the embodiment of the present invention have been described above, the present invention is not limited to the embodiment specifically disclosed and various variations and modifications may be made without departing from the scope of the present invention.

All examples and conditional language provided herein are intended for pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventors to further the art, and are not to be construed as limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of superiority and inferiority of the invention. Although one or more embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention. 

What is claimed is:
 1. A power receiver comprising: a first secondary-side resonant coil, including a first terminal and a second terminal, that receives electric power from a primary-side resonant coil through magnetic field resonance generated between the primary-side resonant coil and the first secondary-side resonant coil; a rectifier circuit, coupled to the first terminal and the second terminal, that rectifies alternating-current power input from the first secondary-side resonant coil; a smoothing circuit coupled to an output side of the rectifier circuit; a pair of output terminals coupled to an output side of the smoothing circuit; a switch, inserted in series on a line between the rectifier circuit and the smoothing circuit, that switches a coupling state of the line, and a drive controller that drives the switch through a first PWM drive pattern determined by a first duty cycle and by a first frequency that is less than or equal to a frequency of the magnetic field resonance, the first duty cycle being set based on a first efficiency of electric power reception of the first secondary-side resonant coil, a first rated power output of a first load coupled to the pair of output terminals, a second efficiency of electric power reception of a second secondary-side resonant coil of another power receiver that receives electric power from the primary-side resonant coil through magnetic field resonance generated between the primary-side resonant coil and the second secondary-side resonant coil, and a second rated power output of a second load to which electric power is supplied from the another power receiver, wherein, when a first value obtained by dividing the first rated power output by the first efficiency of electric power reception is less than a second value obtained by dividing the second rated power output by the second efficiency of electric power reception, the first duty cycle is set to be a predetermined duty cycle that is less than a first initial value, and wherein the predetermined duty cycle is a duty cycle by which a balance between the electric power that the first load receives and the electric power that the second load receives is improved relative to a balance of a case where the first duty cycle is the first initial value.
 2. The power receiver according to claim 1, wherein, when the first value obtained by dividing the first rated power output by the first efficiency of electric power reception is greater than the second value obtained by dividing the second rated power output by the second efficiency of electric power reception, the first duty cycle is set to be the first initial value.
 3. The power receiver according to claim 2, wherein the first initial value is 100%.
 4. A power transmitting system comprising: a first power receiver; a second power receiver; and a power transmitter including the primary-side resonant coil, wherein the first power receiver including: a first secondary-side resonant coil, including a first terminal and a second terminal, that receives electric power from a primary-side resonant coil through magnetic field resonance generated between the primary-side resonant coil and the first secondary-side resonant coil; a rectifier circuit, coupled to the first terminal and the second terminal, that rectifies alternating-current power input from the first secondary-side resonant coil; a smoothing circuit coupled to an output side of the rectifier circuit; a pair of output terminals coupled to an output side of the smoothing circuit; a switch, inserted in series on a line between the rectifier circuit and the smoothing circuit, that switches a coupling state of the line, and a drive controller that drives the switch through a first PWM drive pattern determined by a first duty cycle and by a first frequency that is less than or equal to a frequency of the magnetic field resonance, the first duty cycle being set based on a first efficiency of electric power reception of the first secondary-side resonant coil, a first rated power output of a first load coupled to the pair of output terminals, a second efficiency of electric power reception of a second secondary-side resonant coil of the second power receiver that receives electric power from the primary-side resonant coil through magnetic field resonance generated between the primary-side resonant coil and the second secondary-side resonant coil, and a second rated power output of a second load to which electric power is supplied from the second power receiver, wherein the first power receiver and the second power receiver have a same circuit configuration, wherein in the second power receiver, a switch is driven through a second PWM drive pattern determined by a second duty cycle and by a second frequency that is less than or equal to a frequency of the magnetic field resonance, the second duty cycle being set based on the second efficiency of electric power reception, the second rated power output, the first efficiency of electric power reception, and the first rated power output, wherein, when a second value obtained by dividing the second rated power output by the second efficiency of electric power reception is less than a first value obtained by dividing the first rated power output by the first efficiency of electric power reception, the second duty cycle is set to be a predetermined duty cycle that is less than a second initial value, and wherein the predetermined duty cycle is a duty cycle by which a balance between the electric power that the first load receives and the electric power that the second load receives is improved relative to a balance of a case where the second duty cycle is the second initial value.
 5. The power transmitting system according to claim 4, wherein, when the second value obtained by dividing the second rated power output by the second efficiency of electric power reception is greater than the first value obtained by dividing the first rated power output by the first efficiency of electric power reception, the second duty cycle is set to be the second initial value.
 6. The power transmitting system according to claim 5, wherein the second initial value is 100%.
 7. The power transmitting system according to claim 4, wherein, the first power receiver, the second power receiver, and the power transmitter respectively include a first communication part, a second communication part, and a third communication part, wherein the third communication part of the power transmitter receives from the first communication part of the first power receiver first data that represents the first efficiency of electric power reception and the first rated output and receives from the second communication part of the second power receiver second data that represents the second efficiency of electric power reception and the second rated output, wherein the power transmitter calculates the first value based on the first efficiency of electric power reception and the first rated output represented by the first data that the third communication part receives and calculates the second value based on the second efficiency of electric power reception and the second rated output represented by the second data that the third communication part receives, and wherein the third communication part of the power transmitter transmits to the first communication part of the first power receiver data that represents the first value and transmits to the second communication part of the second power receiver data that represents the second value. 